An earthquake P wave traveling at 8.0 km/s strikes a boundary within the Earth between two kinds of material. If it approaches the boundary at an incident angle of $44 ^\circ$ and the angle of refraction is $33 ^\circ$, what is the speed in the second medium?

VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. Here is the law of refraction which says that the sine of the angle of refraction divided by sine of the angle of incidence equals this wave speed in the second medium divided by the wave speed in the first medium. So, we can multiply both sides by v1 to solve for v2. So, the wave speed in the second kind of material in the earth is the speed of the primary earthquake, p wave, in the first medium times sine of the second angle divided by sine of the first angle. So, that's 8 kilometers per second times sine 33 over sine 44. And since we left this as kilometers per second, our answer will be in kilometers per second. And that's 6.3 kilometers per second.